1. Field of the Invention
The present invention relates to a toner for developing an electrostatic image used for developing an electrostatic latent image formed by an electrophotographic process or an electrostatic recording process, a developer for an electrostatic image, and a process for forming an image.
2. Description of Related Art
A process for visualizing image information through an electrostatic image by an electrophotographic process has been utilized in various fields of art. In the electrophotographic process, an electrostatic image is formed on a photoreceptor by charging and exposing steps, and the electrostatic latent image is visualized by developing it with a developer containing a toner, followed by transferring and fixing steps. The developer used herein includes a two-component developer containing a toner and a carrier and a one-component developer formed solely with a magnetic toner or a non-magnetic toner. The toner is generally produced by a kneading and pulverizing process, in which a thermoplastic resin is melted and kneaded with a colorant, a charge controlling agent and a releasing agent, such as wax, and after cooling, the mixture is finely pulverized and classified. In order to improve the flowability and the cleaning property of the toner, inorganic or organic fine particles may be added to the surface of the toner particles, as required.
In recent years, duplicators and printers utilizing the color electrophotographic process and composite machine thereof with facsimile machines are quickly spread. In the case where moderate gloss upon reproduction of a color image and transparency for obtaining an excellent OHP image are to be realized, it is generally difficult to use a releasing agent, such as wax. Accordingly, a large amount of an oil is applied to a fixing roll for assisting release, but the oil causes sticky feeling of a duplicated image including an OHP image and difficulty in writing on the image with a pen, and uneven gloss feeling also sometimes occurs. Wax including polyethylene, polypropylene and paraffin, which is generally used for monochrome duplication, is more difficult to be used because it impairs the OHP transparency.
Even though the transparency is abandoned, it is difficult that exposure of the releasing agent to the toner surface is suppressed when the toner is produced by the conventional kneading and pulverizing process, and therefore, such problems as considerable deterioration of the flowability and filming on a developing unit and a photoreceptor are caused upon using as a developer.
As an ultimate solution for the problems, a process for producing a toner by such a polymerization process is proposed that an oily phase containing a monomer as a raw material of a resin and a colorant is dispersed in an aqueous phase, and the toner is directly polymerized to form a toner, whereby the wax is encompassed in the interior of the toner to control exposure thereof.
In addition to the above, as a method for enabling intentional control of the toner shape and the surface structure, production processes for a toner by a emulsion polymerization and aggregation process are proposed in Japanese Patent Laid-Open No. 282752/1988 and Japanese Patent Laid-Open No. 250439/1994. In these production processes, the following procedures are generally carried out. A resin dispersion is produced by emulsion polymerization, and separately, a colorant dispersion containing a colorant dispersed in a solvent is produced. They are mixed to form aggregates corresponding to the toner particle diameter, and then they are heated to coalesced, whereby a toner is produced.
These production processes not only realize internal inclusion of the wax, but also facilitate production of a toner of a small diameter, whereby clear image reproduction of high resolution is realized.
When these production processes are employed, the design of the characteristics of the resin becomes considerably important for attaining higher image quality. In order to realize a wide reproduction color gamut, it is necessary that not only the colorant is optimized, but also a gloss image of a certain level or higher is obtained by the melting characteristics of the resin. It is necessary therefore that the elasticity of the resin is decreased by decreasing the molecular weight to lower the melt viscosity thereof upon heating with a heat roll, whereby the resin is designed to increase the flowability thereof. However, when the elasticity is decreased, the adherability to the heat roll is increased, and thus release from the roll becomes difficult in the absence of a fixing oil even though a releasing agent, such as wax, is contained. Furthermore, hot offset at a high temperature due to the lowered molecular weight is liable to be a problem, and as a result, the toner often has a too narrow usable temperature range.
In this case, the fixing behavior becomes extremely sensitive to the temperature fall of a fixing heat roll and the temperature rise upon heating with a heater in continuous printing, and therefore, the temperature control becomes considerably difficult. In practice, influences of quality and thickness of paper on the temperature are to be also considered, whereby the control thereof becomes more complicated. Furthermore, when the molecular weight is decreased, the gloss is increased, but the fixed image becomes mechanically brittle to cause such a problem on durability of the image that the image is damaged upon folding the medium, such as paper.
As described in the foregoing, in order to provide a high quality image by the electrophotographic process and to maintain stable performance of a toner under various kinds of mechanical stress, it is necessary that the selection and the amount of the colorant and the releasing agent are optimized, and exposure of the releasing agent to the surface is suppressed, and also the following factors are extremely important, i.e., improvement of the gloss by optimization of the resin properties, and improvement of the releasing property and suppress of hot offset in the absence of a fixing oil. However, it is the current situation that further improvements are demanded.
Therefore, the invention has been developed to solve the problems associated with the conventional techniques to attain the following targets. The invention is to provide a toner for developing an electrostatic image that has a wide fixable temperature range, is excellent in development and transfer performance and excellent in releasing performance, realizes both glossiness and transparency, and is capable of providing an image (particularly a color image) of a wide color reproduction range having high quality and high durability, a developer for an electrostatic image, and a process for forming an image.
The invention relates to, as one aspect, a toner for developing an electrostatic image containing a binder resin, a colorant and an inorganic metallic salt. An amount of a toluene insoluble component (provided that the colorant, a releasing agent and inorganic and organic insoluble particles are excluded therefrom) is from 0.5 to 10% by weight.
The invention also relates to, as another aspect, a developer for an electrostatic image containing the toner and a carrier.
The invention also relates to, as a further aspect, a process for forming an image. The process contains the steps of: forming an electrostatic latent image on an electrostatic image holding member; developing the electrostatic latent image on a developer holding member with a developer for an electrostatic image containing a toner to form a toner image; transferring the toner image to a transfer material; and fixing the toner image with heat. The toner is the toner for developing an electrostatic image of the invention.
The invention will be described in detail.
The toner for developing an electrostatic image of the invention contains a binder resin, a colorant and an inorganic metallic salt, and an amount of a toluene insoluble component (provided that a colorant, a releasing agent and inorganic and organic insoluble particles are excluded therefrom) is from 0.5 to 10% by weight.
In general, a toner contains, for example, a colorant, such as a pigment, a releasing agent, such as wax, and inorganic and organic insoluble particles, and when the toner is dissolved in a solvent, the pigment, the releasing agent and the inorganic and organic insoluble particles can be separated as a toluene insoluble component. When a crosslinked component is contained in a toner, it is also detected as a toluene insoluble component. In particular, in the case where, upon production thereof, resin particles have polar groups, they easily form ionic crosslinking with metallic ions (inorganic metallic salt) having divalent or more electric charge to form a toluene insoluble component. It has been found that the toluene insoluble component excluding a pigment, a releasing agent and inorganic and organic insoluble particles greatly influences on the melt elastic behavior of the toner. That is, when the amount of the toluene insoluble component contained in the toner is large, gloss is difficult to be obtained, and when it is too small, wrapping on a fixing roll and hot offset due to releasing failure are caused.
From the foregoing standpoint, the toner for developing an electrostatic image of the invention contains a binder resin, a colorant and an inorganic metallic salt, and an amount of a toluene insoluble component (provided that a colorant, a releasing agent and inorganic and organic insoluble particles are excluded therefrom) is from 0.5 to 10% by weight, whereby the fixable temperature range is enhanced, excellent development and transfer performance and excellent releasing performance are provided, and both glossiness and transparency are realized, so as to obtain an image (particularly a color image) of a wide color reproduction range (so-called color gamut) having high quality and high durability.
The toluene insoluble component herein is a component excluding a colorant, a releasing agent and inorganic and organic insoluble particles, and the major component thereof is often a crosslinked component in the toner. Examples of the inorganic insoluble particles include fine particles of silica, titania, magnesia, calcium carbonate, alumina, cerium oxide and strontium titanate, and examples of the organic insoluble particles include fine particles of crosslinked polystyrene, polymethyl methacrylate, copolymers of analogous monomers, and a benzoguanamine resin, and crosslinked resin fine particles.
The amount of the toluene insoluble component (provided that a colorant, a releasing agent and inorganic and organic insoluble particles are excluded therefrom) is from 0.5 to 10% by weight, preferably from 1 to 8% by weight, and more preferably from 2 to 6% by weight. When the amount of the toluene insoluble component is less than 0.5% by weight, the fixable temperature range becomes too narrow due to occurrence of releasing failure and hot offset, and when it exceeds 10% by weight, the gloss of the fixed image becomes too low to narrow the color reproduction range.
The measurement of the toluene insoluble component can be carried out the following procedures.
Measurement of Toluene Insoluble Component
(1) About 0.3 g of a sample (toner) is weighed precisely to a unit of 0.1 mg directly to a 25-ml flask (weight A).
(2) 20 g of toluene is put on the flask, and after sealing hermetically, the sample is dissolved at room temperature around 20xc2x0 C. The solution obtained by dissolving the sample in toluene is then transferred to a 40-ml separation tube for centrifugal separation. Another 20 g of toluene is put in the empty flask to wash the interior thereof, and the resulting solution is also put in the separation tube for centrifugal separation. The separation tube is sealed and subjected to centrifugal separation (at xe2x88x9210xc2x0 C. and 18,000 rpm for 20 minutes).
(3) A tare of an aluminum plate is precisely measured (weight B).
(4) After allowing to stand the separation tube until it is at room temperature, 5 g of a supernatant liquid in the separation tube is weighed with a pipette on the aluminum plate having been precisely weighed.
(5) The aluminum plate is heated to 80xc2x0 C. to evaporate the toluene component, and the sample is completely dried in a vacuum dryer and weighed (weight C).
After carrying out the foregoing procedures (1) to (5), the amount of the toluene insoluble component excluding a pigment, a releasing agent and inorganic and organic insoluble particles is calculated by the following equation.             toluene      ⁢              xe2x80x83            ⁢      insoluble      ⁢              xe2x80x83            ⁢      component      ⁢              xe2x80x83            ⁢              (        %        )              =                                                      (                                                                    (                                          A                      -                                                                        (                                                      C                            -                            B                                                    )                                                xc3x97                        8                                                              )                                    /                  A                                xc3x97                100                            )                        -                          (                                                pigment                  ⁢                                                            xe2x80x83                                        ⁢                                          xe2x80x83                                                        (                  %                  )                                +                                  releasing                  ⁢                                      xe2x80x83                                    ⁢                  agent                  ⁢                                      xe2x80x83                                    ⁢                                      (                    %                    )                                                  +                                                                                                    inorganic              ⁢                              xe2x80x83                            ⁢              and              ⁢                              xe2x80x83                            ⁢              organic              ⁢                              xe2x80x83                            ⁢              insoluble              ⁢                              xe2x80x83                            ⁢              particles              ⁢                              xe2x80x83                            ⁢                              (                %                )                                      )                                ⁢      xe2x80x83  
The amounts of a colorant (pigment), a releasing agent and inorganic and organic insoluble particles can be obtained from the values in part by weight upon weighing in production of the sample or measured from analytical values of fluorescent X-ray analysis, atomic absorption spectrometry analysis or differential scanning calorimetry.
The toluene insoluble component can be controlled, for example, by controlling the amount of an inorganic metallic salt that is added upon aggregation of the resin particles, the colorant and the releasing agent, and by adjusting appropriately the concentration or the acid value of releasing polar groups in the resin particles and the pH conditions upon coalescing after reaching the target particle diameter through aggregation. In particular, it is considered that the amount of the toluene insoluble component is controlled by the number of groups forming ion crosslinking and the dissociation conditions thereof upon formation. When the amount of the inorganic metallic salt is increased, there is a tendency that the amount of the toluene insoluble component is increased, and when it is decreased, there is a tendency that the amount of the toluene insoluble component is decreased.
The toner for developing an electrostatic image of the invention preferably has a shape factor SF1 of 140 or less to obtain excellent charge characteristics, cleaning property and transfer property, and it is more preferably from 110 to 135. When the shape factor SF1 exceeds 140, the transfer efficiency from the electrostatic image holding member holding the toner image to the transfer material is lowered to impair the reliability of image quality. The cleaning property referred herein is that with respect to cleaning by the blade method, which is the most popular method.
The shape factor SF1 is obtained in the following manner. An optical micrograph of the toner scattered on slide glass is imported to a Luzex image analyzer through a video camera, and the peripheral maximum length (ML) and the projected area (A) are measured for 50 or more toner particles. The shape factor SF1 is a value obtained therefrom by the equation (square of maximum length)/(projected area)=ML2/A.
The toner for developing an electrostatic image of the invention preferably has a surface property index represented by the following equation (A) of 2.0 or less because good transfer property is obtained, and in particular, uniform and high image quality with high transfer efficiency is realized for paper and a transfer material having a large surface roughness, and it is more preferably from 1.0 to 2.0, and further preferably from 1.0 to 1.8.
surface property index=(measured specific surface area)/(calculated specific surface area)xe2x80x83xe2x80x83(A)
The calculated specific surface area herein is obtained by the following equation.
calculated specific surface area=6xcexa3(nxc3x97R2)/(xcfx81xc2x7xcexa3(nxc3x97R3))
wherein n represents the number of particles of the toner present in a channel of a Coulter counter, R represents a channel particle diameter (xcexcm) in the Coulter counter, and xcfx81 represents the toner density (g/cm2) and the Coulter counter has 16 channels (divided number: dividing the area of from 1 to 50 xcexcm into 16 pieces).
The measured specific surface area is measured by the gas adsorption/desorption method, and it can be obtained by measuring the Langmuir specific surface area. As the measuring apparatus, for example, Coulter Model SA3100 (produced by Beckman Coulter, Inc.) and Gemini 2360/2375 (produced by Shimadzu Corp.) can be used.
As a method for controlling the surface property index represented by the equation (A), for example, it can be controlled by adjusting appropriately the temperature and the pH upon fusing and coalescing the aggregated particles containing the resin particles.
The toner for developing an electrostatic image of the invention preferably has an apparent weight average molecular weight in a range of from 15,000 to 55,000, and more preferably in a range of from 20,000 to 48,000. When the weight average molecular weight is lower than 15,000, there are some cases where the cohesive force of the binder resin is lowered to deteriorate the oilless releasing property, and when it exceeds 55,000, there are some cases where the smoothness upon fixing becomes poor while the oilless releasing property is good, whereby the glossiness is lowered.
The toner for developing an electrostatic image of the invention preferably has a glass transition point Tg in a range of from 45 to 65xc2x0 C., and more preferably in a range of from 48 to 60xc2x0 C. When Tg is lower than 45xc2x0 C., the cohesive force of the binder resin itself at a high temperature range is lowered, and hot offset is liable to occur upon fixing, and when it exceeds 65xc2x0 C., there are some cases where sufficient fusion cannot be obtained to lower the glossiness of the fixing sheet.
The toner for developing an electrostatic image of the invention preferably has an accumulated volume average particle diameter D50V in a range of from 3.0 to 9.0 xcexcm, more preferably in a range of from 3.0 to 8.0 xcexcm, and in the invention further preferably in a range of from 4 to 6 xcexcm. In particular, when D50V is in a range of from 4 to 6 xcexcm, it is preferred from the standpoint that uniform glossiness can be obtained. When D50V is lower than 3.0 xcexcm, there are some cases where the charging property is insufficient, and the developing property is lowered. When it exceeds 9.0 xcexcm, the resolution property of the image is lowered.
The toner for developing an electrostatic image of the invention preferably has a volume average particle size distribution index GSDv of 1.30 or less. When GSDv exceeds 1.30, there are some cases where the resolution property is lowered, which becomes a factor of image defects, such as scattering of the toner and fogging.
The accumulated average particle diameter and the average particle size distribution index can be calculated in the following manner. The particle size distribution is measured, for example, by a measuring apparatus, such as Coulter Counter TAII (produced by Nikkaki Co., Ltd.) and Multisizer II (produced by Nikkaki Co., Ltd.). Based on the particle size distribution, the values of volume and number for the divided particle size areas (divided number: dividing the area of from 1 to 50 xcexcm into 16 pieces) are obtained, and accumulated distribution curves thereof are drawn from the small particle size side. The particle diameters at the volume and the number of accumulation of 16% are defined as D16V and D16P, respectively, the particle diameters at the volume and the number of accumulation of 50% are defined as D50V and D50P, respectively, and the particle diameters at the volume and the number of accumulation of 84% are defined as D84V and D84P, respectively. By using these values, the volume average particle size distribution index (GSDv) is calculated as (D84V/D16V)1/2, and the number average particle size distribution index (GSDp) is calculated as (D84P/D16P)1/2.
The toner for developing an electrostatic image of the invention is preferably produced by the following wet production process because a toner having a small diameter and the sharp particle size distribution described in the foregoing can be obtained. The wet production process contains steps of: aggregating a particle group in a dispersion containing the particle group containing at least resin particles, and an inorganic metallic salt, to obtain aggregated particles; and heating the aggregated particles to coalesce them. Such is suitable from the viewpoint that high-image quality full-color images can be formed. Particularly, in this wet production process, in the case where the amount of the toluene insoluble component is increased by aggregating the resin particles with the inorganic metallic salt, the toluene insoluble component is uniformly incorporated into the toner particles in comparison to the conventional toners produced by the pulverization process, whereby fluctuation in composition among the toner particles is reduced. In the case where crosslinking is effected upon melting and kneading in the conventional pulverization process, because the inorganic metallic particles are dispersed in the resin, crosslinked matters are partially formed, whereby parts having a large gel content (toluene insoluble component) are not pulverized to form a toner having a large gel content and a toner having a small gel content.
In the foregoing process step for obtaining the aggregated particles, in addition to the particle group containing the resin particles, and the inorganic metallic salt, a colorant (particles) and a releasing agent (particles) may be used in the particle group depending on necessity. Known internal additives, such as a charge controlling agent, may also be used as additives.
The inorganic metallic salt can be obtained by dissolving an ordinary inorganic metallic compound or a polymer thereof in the resin particle dispersion. A metallic element constituting the inorganic metallic salt is having a charge of divalent or more belonging to the 2A, 3A, 4A, 5A, 6A, 7A, 8, 1B, 2B and 3B groups of the periodic table (long form periodic table), and it is preferably one that is dissolved in the form of ions in the aggregated system of the resin particles, i.e., a so-called water soluble metallic salt. Specific and preferred examples of the inorganic metallic salt include metallic salts, such as calcium chloride, calcium nitrate, barium chloride, magnesium chloride, zinc chloride, aluminum chloride and aluminum sulfate, and an inorganic metallic salt polymer, such as polyaluminum chloride, polyaluminum hydroxide and polycalcium sulfide. Among these, an aluminum salt and a polymer thereof are particularly preferred. In general, in order to obtain a shaper particle size distribution, the valence number of the inorganic metallic salt is preferably larger, i.e., divalent is better than monovalent, and trivalent is better than divalent, and in the case of the same valence number, an inorganic metallic salt polymer is more preferred.
Examples of the binder resin used as the resin fine particles include a homopolymer and a copolymer of a vinyl monomer, e.g., a styrene compound, such as styrene and parachlorostyrene, a vinyl ester, such as vinylnaphthalene, vinyl chloride, vinyl bromide, vinyl fluoride, vinyl acetate, vinyl propionate, vinyl benzoate and vinyl butyrate, a methylene aliphatic carboxylate ester, such as methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, dodecyl acrylate, n-octyl acrylate, 2-chloroethyl acrylate, phenyl acrylate, methyl xcex1-chloroacrylate, methyl methacrylate, ethyl methacrylate and butyl methacrylate, acrylonitrile, methacrylonitrile, acrylamide, a vinyl ether, such as vinyl methyl ether, vinyl ethyl ether and vinyl isobutyl ether, a monomer having an N-containing polar group, such as N-vinylpyrrol, N-vinylcarbazole, N-vinylindol and N-vinylpyrrolidone, metacrylic acid, acrylic acid, cinnamic acid, and a vinyl carboxylic acid, such as carboxyethyl acrylate, and/or various kinds of polyester, and various kinds of wax may also be used in combination.
In the case where the binder resin is formed from a vinyl monomer, it can be produced in such a manner that emulsion polymerization is carried out by using an ionic surfactant to produce a resin particle dispersion. In the case of other resins that are oleophilic and are dissolved in a solvent having relatively low solubility in water, the resin is dissolved in the solvent and dispersed in the form of particles in water along with an ionic surfactant and a polymer electrolyte by using a disperser, such as a homogenizer, followed by evaporating the solvent by heating or under reduced pressure, whereby a resin particle dispersion can be obtained.
The resin particles in the resin particle dispersion preferably have a center diameter (median diameter) of 1 xcexcm or less, more preferably from 50 to 400 nm, and further preferably from 70 to 350 nm.
The center diameter (median diameter) of the resin particle can be measured, for example, with a laser diffraction particle size distribution measuring apparatus (LA-700, produced by Horiba, Ltd.).
As the colorant (particles), the following materials can be preferably used.
Examples of a black pigment include carbon black, copper oxide, manganese dioxide, aniline black, activated carbon, non-magnetic ferrite and magnetite.
Examples of a yellow pigment include chrome yellow, zinc yellow, yellow iron oxide, cadmium yellow, chrome yellow, hansa yellow, hansa yellow 10G, benzidine yellow G, benzidine yellow GR, suren yellow, quinoline yellow and permanent yellow NCG.
Examples of an orange pigment include red chrome yellow, molybdenum orange, permanent orange GTR, pyrazolone orange, vulkan orange, benzidine orange G, indanthrene brilliant orange RK and indanthrene brilliant orange GK.
Examples of a red pigment include red iron oxide, cadmium red, red lead, mercury sulfide, watchyoung red, permanent red 4R, lithol red, brilliant carmine 3B, brilliant carmine 6B, Du Pont oil red, pyrazolone red, rhodamine B lake, lake red C, rose bengal, eosine red and alizarine lake.
Examples of a blue pigment include iron blue, cobalt blue, alkali lake blue, victoria blue lake, fast sky blue, indanthrene blue BC, aniline blue, ultramarine blue, calco oil blue, methylene blue chloride, phthalocyanine blue, phthalocyanine green and malachite green oxalate.
Examples of a violet pigment include manganese violet, fast violet B and methyl violet lake.
Examples of a green pigment include chromium oxide, chromium green, pigment green, malachite green lake and final yellow green G.
Examples of a white pigment include zinc flower, titanium oxide, antimony white and zinc sulfide.
Examples of a body pigment include barite powder, barium carbonate, clay, silica, white carbon, talc and alumina white.
Examples of a dye include various kinds of dye including basic, acidic, dispersed and direct dyes, for example, nigrosine, methylene blue, rose bengal, quinoline yellow and ultramarine blue.
A magnetic toner can be obtained by using a magnetic material as the whole or part a black colorant among the colorants. A magnetic material may be added separately from the colorant. The magnetic material used herein is a substance that is magnetized in a magnetic field, and specific examples thereof are compounds such as ferromagnetic powder, such as iron (including reduced iron), cobalt, nickel and manganese, ferrite and magnetite. In the case where the toner is obtained in an aqueous phase, it is necessary to pay attention to the aqueous phase transition property of the magnetic material, and it is preferred that the surface of the magnetic material is previously modified, for example, subjected to a hydrophobic treatment.
These colorants are used solely or as a mixture. A dispersion of colorant particles is prepared by dispersing the colorant by using, for example, a revolving shearing homogenizer, a media disperser, such as a ball mill, a sand mill and an attritor, or a high pressure counter collision type disperser. The colorant may be dispersed in an aqueous system with a homogenizer by using a surfactant having polarity. In particular, it is preferred that the colorant is selected in view of hue, chroma, brightness, weather resistance, OHP transparency and dispersibility in the toner.
It is preferred that the colorant is added in an amount of from 4 to 15% by weight based on the total weight of the solid content constituting the toner, and in the case where a magnetic material is used as a black colorant, it is preferably added in an amount of from 12 to 240% by weight, which is different from those for the other colorants. The mixed amount of the colorant is the necessary amount for obtaining the coloring property upon fixing, and therefore, it is not limited to the foregoing ranges. The colorant (colorant particles) in the toner preferably has a center diameter (median diameter) of from 100 to 330 nm, and the OHP transparency and the coloring property can be assured by using the range.
The center diameter of the colorant (colorant particles) can be measured, for example, with a laser diffraction particle size distribution measuring apparatus (LA-700, produced by Horiba, Ltd.).
Examples of the releasing agent (particles) include a low molecular weight polyolefin, such as polyethylene, polypropylene and polybutene, a silicone exhibiting a softening point upon heating, an aliphatic amide, such as oleic amide, erucic amide, recinoleic amide and stearic amide, vegetable wax, such as carnauba wax, rice wax, candelilla wax, haze wax and jojoba oil, animal wax, such as yellow beeswax, mineral or petroleum wax, such as montan wax, ozokerite, ceresin, paraffin wax, microcrystalline wax and Fischer-Tropsch wax, and denatured materials thereof. The wax is substantially not dissolved in a solvent, such as toluene, around room temperature, or even through it is dissolved, only a slight amount thereof is dissolved. A dispersion of the wax can be obtained in such a manner that the wax is dispersed in water along with an ionic surfactant or a polymer electrolyte, such as a polymer acid and a polymer base, and it is heated to a temperature higher than the melting point thereof and dispersed into fine particles with a homogenizer or a pressure discharge disperser (Gaulin Homogenizer, produced by Gaulin Corp.) capable of applying a strong shearing force, whereby a particle dispersion of 1 xcexcm or less can be prepared.
The particle diameter of the releasing agent particles can be measured, for example, with a laser diffraction particle size distribution measuring apparatus (LA-700, produced by Horiba, Ltd.). Upon using the releasing agent, it is preferred that after aggregating the resin particles, the colorant particles and the releasing agent particles, the resin particle dispersion is further added to attach the resin particles on the surface of the aggregated particles, in order to assure the charging property and the durability.
The releasing agent is preferably added (contained) in an amount of 10% by weight or more based on the total weight of the solid content constituting the toner, in order to assure the releasing property of the fixed image in the oilless fixing system, and it is more preferably in a range of from 10 to 25% by weight.
As the charge controlling agent, various kinds of charge controlling agents, which are ordinarily used, such as a quaternary ammonium salt compound, a nigrosine compound, a dye containing a complex of aluminum, iron or chromium, and a triphenylmethane pigment, can be used, and such materials that are difficult to be dissolved in water are preferred from the standpoint of control of the ion intensity, which influences on the stability upon aggregation and uniting, and reduction of contamination due to waste water.
A surfactant can be used upon emulsion polymerization and seed polymerization of the binder resin, dispersion of the colorant (particles), dispersion of resin fine particles, dispersion of the releasing agent (particles), aggregation and stabilization of the aggregated particles. Specific examples of the surfactant include an anionic surfactant, such as sulfate ester series, sulfonate series, phosphate ester series and soap series, and a cationic surfactant, such as amine salt type and quaternary ammonium salt type. It is also effective to use a nonionic surfactant, such as polyethylene glycol series, alkylphenol ethylene oxide series and polyvalent alcohol series, in combination. As the dispersion method, those are generally employed, such as a revolving shearing homogenizer, a media disperser, such as a ball mill, a sand mill and a dynomill.
Subsequent to the process step for obtaining the aggregated particles described in the foregoing, a process step for fusing the aggregated particles by heating (fusing and coalescing step) is carried out. After completing the fusing and coalescing step, a washing step, a solid-liquid separating step and a drying step are arbitrarily carried out depending on necessity, so as to obtain the desired toner (toner particles). In the washing step, it is preferred to carry out sufficient washing with ion exchanged water from the standpoint of charging property. The solid-liquid separating step is not particularly limited, suction filtration and pressure filtration are preferred from the standpoint of productivity. The drying step is also not particularly limited, and freeze-drying, flash jet drying, flowing drying and vibration flowing drying are preferably employed from the standpoint of productivity.
With respect to the production process of a toner by a wet production process using an inorganic metallic salt, for example, the emulsion aggregation process using a water soluble inorganic metallic salt having divalent or more electric charge disclosed in Japanese Patent No. 3,107,062 can be preferably employed, in which resin particles and other particles are aggregated in an aqueous medium using an inorganic metallic salt having a divalent or more electric charge, the pH of the aggregated particle dispersion is adjusted to a range of from 2 to 14, and preferably from 3 to 10, and then, after stabilizing the aggregated particles, they are coalesced by heating.
As similar to the ordinary toners, in order to apply flowability and to improve the cleaning property, it is possible that the toner for developing an electrostatic image of the invention is dried, and fine particles are added to the surface of the toner particles (so-called external additive) in a dry state under application of a sharing force. Examples of the fine particles include inorganic fine particles, such as silica, alumina, titania and calcium carbonate, and resin fine particles, such as a vinyl resin, polyester and silicone.
In the case where the fine particles are attached to the toner surface (external additive) in water, as examples of the inorganic fine particles, all the materials that are ordinarily used as an external additive, such as silica, alumina, titania, calcium carbonate, magnesium carbonate and tricalcium phosphate, can be used after dispersing with an ionic surfactant, a polymer acid or a polymer base.
(Developer for Electrostatic Image)
In the case where a magnetic material is added to the toner for developing an electrostatic image of the invention, or in the case where a magnetic material is added thereto as the whole or part of the black colorant thereof, the toner can be used as the one-component developer for an electrostatic image of the invention. The toner for developing an electrostatic image of the invention can also be used as the two-component developer for an electrostatic image of the invention by adding a carrier thereto.
The carrier is not particularly limited, and examples thereof include those having been known in the art. Among these, a resin-coated carrier is preferably used. As the resin-coated carrier, such known carriers can be used as the resin-coated carriers disclosed in Japanese Patent Laid-Open No. 39879/1987 and Japanese Patent Laid-Open No. 11461/1981. Examples thereof include the following resin-coated carriers. Examples of core particles of the carriers include ordinary ones, such as iron powder, ferrite and magnetite granulated materials, and the average particle diameter thereof is generally about from 30 to 200 xcexcm. Examples of a resin coated on the core particles include a homopolymer of a monomer, e.g., a styrene compound, such as styrene, parachlorostyrene and a-methylstyrene, an xcex1-methylene aliphatic monocarboxylate, such as methyl acrylate, ethyl acrylate, n-propyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, n-propyl methacrylate, lauryl methacrylate and 2-ethylhexyl methacrylate, a nitrogen-containing acrylic compound, such as dimethylaminoethyl methacrylate, a vinyl nitrile, such as acrylonitrile and methacrylonitrile, a vinylpyridine, such as 2-vinylpyridine and 4-vinylpyridine, a vinyl ether, such as vinyl methyl ether and vinyl isobutyl ether, a vinyl ketone, such as vinyl methyl ketone, vinyl ethyl ketone and vinyl isopropenyl ketone, an olefin, such as ethylene and propylene, and a vinyl series fluorine-containing monomer, such as vinylidene fluoride, tetrafluoroethylene and hexafluoropropylene, a copolymer of two or more of these monomers, a silicone, such as methyl silicone and methylphenyl silicone, polyester containing bisphenol or glycol, an epoxy resin, a polyurethane resin, a polyamide resin, a cellulose resin, a polyether resin, and a polycarbonate resin. These resins may be used solely or in combination of two or more kinds thereof. The amount of the coating resin is generally about from 0.1 to 10 parts by weight based on the core particles, and preferably from 0.5 to 3.0 parts by weight. Upon producing the carrier, a heating kneader, a heating Henschel mixer and a UM mixer can be used, and depending on the amount of the coating resin, a heating fluidized rolling bed and a heating kiln may also be used. The mixing ratio of the toner for developing an electrostatic image of the invention and the carrier is not particularly limited and can be appropriately selected depending on purposes.
(Process for Forming Image)
The process for forming an image of the invention contains steps of: forming an electrostatic latent image on a electrostatic image holding member; developing the electrostatic latent image on an electrostatic image holding member with a developer containing a toner to form a toner image; transferring the toner image to a transfer material; and fixing the toner image with heat, in which the toner for developing an electrostatic image of the invention is used as the toner.
In the process for forming an image of the invention, the respective steps themselves are those having been known and disclosed, for example, in Japanese Patent Laid-Open No. 40868/1981 and Japanese Patent Laid-Open No. 91231/1974, which can be applied to the invention. The process for forming an image of the invention can be practiced by using an image forming apparatus having been known, such as a duplicator and a facsimile machine.